1. Field of the Invention
Embodiments described herein relate generally to a network system formed as, for example, a ring type.
2. Description of the Related Art
Conventionally, a ring-type network system is used as a network system that periodically transmits data to a plurality of terminal apparatuses. Such a network system is preferably capable of transmitting data that should be periodically transmitted without any loss even when, for example, a failure has occurred on part of the transmission path. In addition, using an apparatus employing Ethernet® for the physical layer and the data link layer as a network transmission apparatus is advantageous for the cost and member availability from the viewpoint of the degree of technical maturity and popularization. If an error has occurred on the apparatus or transmission line in the network system using such a network transmission apparatus, the transmission path is changed to avoid the error.
However, the conventional network system has the following problems. That is, an apparatus for monitoring the presence/absence of an error is necessary. Switching to change the path after the occurrence of an error is time-consuming. To shorten the switching time, the transmission apparatus becomes complex. Data may be lost at the time of switching. In addition, the network system may have physically duplexed transmission lines to improve the reliability of transmission. However, installing a plurality of transmission lines is expensive.